(1) Field of the Invention
The present invention relates to a lighting method and apparatus for a high-pressure discharge lamp, and a high-pressure discharge lamp apparatus.
(2) Description of Related Art
Light sources generally in use for a liquid crystal projector are high-pressure discharge lamps such as high-pressure mercury lamps. As liquid crystal projectors are reduced in size and more widely used in a general household environment, it is now required to make some adjustment so as to prevent the screen from being too bright depending on brightness of the environment and the type of image to be projected. One liquid crystal projector designed to meet such requirement has a so-called dimming function (See, for example JP 2000-131668-A). Dimming function is to adjust the brightness of a high-pressure discharge lamp as well as to save power consumption by operating the lamp with a lower power than the rated power. Hereinafter, lamp operation by supplying a lower power than the rated power is referred to as “dimmed-state operation”.
However, there is a problem found through the study conducted by inventors of the present invention on the dimmed-state operation of a conventional high-pressure discharge lamp and a conventional lighting apparatus. That is, a temperature rise of a lighting apparatus under dimmed-state operation tends to be greater in comparison with a temperature rise under rated-power operation. This greater temperature rise is ascribable to excessive load imposed on the lighting apparatus, and means that the lighting apparatus needs to be upsized and/or provided with enhanced cooling. These requirements, however, contradict a demand for a downsized, quieter projector.